The stock is the key part of this deal. Its value is derived from the $6.5 billion common valuation after a recent purchase of employee stock by the Russian investment group DST. But what’s really interesting about the stock is that these are options that vest over a set period of time (“several years,” says WSJ), just as employees in the company get. Compared to the Parakey deal in July 2007, in which the company got only cash and no stock, this seems like a pretty nice deal (assuming that Facebook’s stock eventually pans out, of course).

Another interesting question about this is what Benchmark Capital, FriendFeed’s outside investor, got? It’s certainly possible that they’re taking the cash, while the FriendFeed employees take the stock. Benchmark invested a small part of the company’s $5 million round in early 2008, so a $15 million exit would be pretty solid. But that’s all just speculation, it’s hard to know what Benchmark is getting for sure.

What else is interesting about this $50 million number is that it is 1/10th of what Facebook was apparently willing to pay for Twitter late last year. One big hold up in that deal was that Facebook was offering mostly stock, while Twitter wanted more cash (we heard roughly 20% would have been cash, with the rest coming in stock). Another big problem was that the stock Facebook was offering Twitter was apparently valued based on the ridiculous $15 billion valuation after Microsoft’s investment in October of 2007. The $6.5 billion common stock valuation seems much more reasonable. Too bad for Twitter.